This application is based on application No. Hei 11-147823 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention pertains to a lens drive device capable of manual focus (MF) adjustment and auto-focus (AF) adjustment, and more particularly, to a camera equipped with interchangeable photographing lenses.
2. Description of the Related Art
In conventional AF single-lens reflex cameras, the photographing lens unit equipped with lenses is interchangeable. A photographing lens unit has a lens coupler, and the positions of the photographing lenses are changed via the rotation of the lens coupler. A lens drive motor is located inside the camera main body. The coupler on the side of the camera main body, which is connected to the lens drive motor by means of gears, protrudes from the body mount.
An encoder that detects the amount of rotation of the lens drive motor is also located inside the camera main body. When the photographing lens unit is mounted to the camera main body, a coupler engages with a lens coupler. Consequently, the drive force of the lens drive motor is transmitted to the photographing lenses, and prescribed pulse signals are generated from the encoder so that the photographing lenses will be moved to prescribed positions in an auto-focus operation.
The photographing lens unit has a focusing ring. Manual focusing is preformed by turning the focusing ring to change the positions of the photographing lenses. During manual focusing, if the photographing lenses and the lens drive motor are connected via the couplers, a load is placed on the operation of the focusing ring, which reduces operability.
Therefore, a camera has been proposed that is equipped with a mechanism that retracts the coupler from the lens coupler during manual focusing (U.S. Pat. No. 4,724,454). This mechanism disconnects the photographing lenses and the lens drive motor so that the load on the focusing ring during operation may be reduced.
However, if the connection between the lens coupler and the coupler is terminated during manual focusing, when the photographing lenses are moved by operating the focusing ring, no pulse signals are generated by the encoder. Consequently, the problem arises that the object distance is not detected because the positions of the photographing lenses are unclear, and as a result control regarding the aperture and the flash based on light measurement cannot be performed at an optimal level.
In addition, when performing auto-focusing after manual focusing, the absolute position must be detected after the photographing lenses are moved to the reference positions. Because of this necessity, there has been the problem that auto-focusing is time-consuming, resulting in poor operability.
The object of the present invention is to provide a lens drive device that makes it possible to detect the positions of the photographing lenses during manual focusing, and that improves the operability of the camera.
In order to attain this object, the present invention comprises a lens drive device that is located inside a camera main body and can drive the photographing lenses that are interchangeably mounted to the camera main body, said lens drive device having a coupler that transmits the drive force to the photographing lenses, a drive motor that rotates and drives the coupler, a clutch mechanism that connects and disconnects the coupler and the drive motor, and an encoder that detects the amount of rotation of the coupler while the coupler and the drive motor are disconnected by means of the clutch mechanism.
Using this construction, the photographing lenses are interchangeably mounted to the camera main body by means of a photographing lens unit, etc. The photographing lens unit has a lens coupler that is connected to the photographing lenses, and the photographing lens unit is connected to the camera main body, with the coupler engaging with the lens coupler. During auto-focusing in which the drive motor and the coupler are connected by means of the clutch mechanism, the drive force of the lens drive device is transmitted to the photographing lenses via the coupler and the lens coupler, such that the photographing lenses are driven. During manual focusing in which the drive motor and the coupler are disconnected by means of the clutch mechanism, the photographing lenses are moved such that the amount of rotation of the coupler may be detected by the encoder.
The encoder comprises a contact encoder that has a pulse generating pattern that rotates together with the coupler, as well as a contact that comes into contact with the pulse generating pattern and generates pulse signals. Using this construction, during manual focusing, the photographing lenses are moved such that the contact encoder having a contact can detect the amount of rotation of the coupler.
Alternatively, the encoder comprises a non-contact encoder having a pulse generating pattern that rotates together with the coupler and a non-contact detector that detects the pulse generating pattern and generates pulse signals. Using this construction, during manual focusing, the photographing lenses is moved such that the non-contact encoder having an optical or magnetic detector can detect the amount of rotation of the coupler.
The encoder comprises a contact encoder having a first pulse generating pattern that rotates together with the coupler and a contact that comes into contact with the first pulse generating pattern and generates pulse signals, as well as a non-contact encoder having a second pulse generating pattern that rotates together with the coupler and a non-contact detector that detects the second pulse generating pattern and generates pulse signals.
Using this construction, during manual focusing, the photographing lenses are moved such that the contact encoder having a contact or the non-contact encoder having a detector can detect the amount of rotation of the coupler.
In addition, the contact encoder detects the amount of rotation of the coupler when the camera has been in a standby state while waiting for the coupler to start rotating, and the non-contact encoder detects the amount of rotation of the coupler immediately after it is disconnected from the drive motor after it rotates by means of the drive motor.
Using this construction, during manual focusing after the camera has been in a standby state, the photographing lenses are moved such that the contact encoder can detect the amount of rotation of the coupler, and during manual focusing immediately after auto-focusing, the photographing lenses are moved such that the non-contact encoder can detect the amount of rotation of the coupler. The camera returns to the standby state if manual focusing is not performed for a prescribed period of time.
The amount of rotation of the coupler is detected by the non-contact encoder while the coupler and the drive motor are connected by means of the clutch mechanism. Using this construction, during auto-focusing, in which the drive motor and the coupler are connected by means of the clutch mechanism, the photographing lenses are moved such that the non-contact encoder can detect the amount of rotation of the coupler.
These and other objects, advantages and features of the invention will become apparent from the following description thereof taken in conjunction with the accompanying drawings which illustrate specific embodiment of the invention.